1. Field of the Invention
The present invention relates to a telephone apparatus system, connected to an ISDN (Integrated Service Digital Network) and a public service telephone network, for performing verbal communication control at least between a connected line and accommodated extensions.
2. Description of the Prior Art
As shown in FIG. 5, in a conventional key telephone apparatus, a main apparatus 60 accommodates a plurality of office lines (52 and 53) connected to a public service telephone network (analog telephone network; PSTN) 51, and performs speech path control between a connected line and extension telephone sets (54 to 56) connected to the main apparatus 60 or between extension telephone sets.
For this reason, the accommodated office lines are connected to only the PSTN 51. In this case, users cannot enjoy a variety of high-level services of an ISDN.
Power supply to the extension telephone sets (54 to 56) connected to the accommodated office lines is normally performed by the main apparatus 60. For this reason, the operation of the main apparatus 60 is stopped upon a power failure, and the functions such as an exchange processing function of the entire system are stopped as well as power supply to the extension telephone sets (54 to 56).
In order to allow services of an ISDN, as shown in FIG. 6, a main apparatus 70 accommodates a plurality of office lines (62 and 63) connected to an ISDN 61, and performs speech path control between a connected office line and extension telephone sets (64 to 66) connected to the main apparatus 70 or between the extension telephone sets.
In this case, however, the functions of the main apparatus 70 and power supply to the extension telephone sets 64 to 66 are stopped upon a power failure, and hence, the functions of the entire system are stopped.